1. Field of the Invention
The present invention is generally related to the field of electroactive actuators. More specifically, it relates to an electroactive actuator having at least one layer of non-uniform thickness.
2. Description of the Related Art
Actuation devices are used for many applications, including aerospace, fluid flow and biomedical. Space applications include robotics, miniature rovers, and the shaping, tuning, positioning, controlling and deforming of membrane structures. Membrane inflatable and deployable space structures are used by the government and commercially as reflectors, antennas, solar arrays, satellites, solar sails, etc. Although actuation devices are widely used, many challenges exist which limit their performance for high precision applications. Factors affecting precision include surface smoothness, deviation from desired surface profile, surface deformations due to thermal fluctuations, and accurate membrane positioning. Additionally, hydrofoils and airfoils that can optimize their surface shape at varying flow rates are desirable to, for example, increase lift, reduce noise levels, lower vibrations and reduce drag. Other potential uses of actuation devices include precise positioning of display panels and optical index layers. To operate most effectively in the aforementioned applications, actuation devices require sufficient force and strain, and often need to produce complex motions that may include both bending and torsion.
Conventional piezoelectric ceramic, polymer, and composite actuators (including piezoelectric, electrostrictive, and electrostatic) lack the combination of sufficient strain and force to most effectively perform the aforementioned functions. Previous concepts for shaping and tuning membrane structures have primarily involved the use of piezoelectric ceramic materials. These ceramic piezoelectrics have the major problems of large mass, high density, low strain and high brittleness. Generally, piezoceramics also need additional mechanical devices to achieve a shaping, tuning, positioning, controlling or deforming function. In contrast to electroceramics, electroactive polymers are emerging as new actuation materials due to their enhanced strain capabilities.
Electrostrictive polymer-polymer actuators or other electroactive polymer actuators that provide enhanced strain capabilities can shape, tune, position, control and deform membrane structures, as well as perform in other applications, in ways not previously possible with other materials. An example of such an electrostrictive polymer-polymer actuator is described in the patent application entitled “Polymer-Polymer Bilayer Actuator”, Ser. No. 09/696,524, filed Oct. 23, 2000, hereby incorporated by reference. The greater strain capability provides further possibilities for small-scale applications and integration into skin surfaces. The electroactive actuators can coincide with specific contours to optimize, for example, shapes for fluid flow, reflection and other membrane uses.
Existing devices capable of providing complex motion response utilize surface electrode patterning and/or polymer laminates having tailored lamina properties and orientations, such as described in U.S. Pat. No. 4,868,447. It is desirable to obtain complex motion response without requiring tailored surface electroding or laminate design.